The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Hydraulic fracturing is one of the techniques used in enhanced hydrocarbon recovery. Hydraulic fracturing involves pumping a fracturing fluid into an injection well and against the face of the formation at a pressure and flow rate at least sufficient to overcome the in-situ stresses and to initiate and/or extend a fracture or fractures into the formation. The injection well is at a distance from the production well and a fracturing fluid is injected to maintain reservoir pressure and help displace oil towards the production wells.
Referring to FIG. 1, in a conventional hydraulic fracturing method, a fracturing fluid (not shown) which carries proppant particles 10 is injected into an injection well (not shown) to initiate a fracture 12 in the hydrocarbon-containing formation 14. The fracturing fluid is generally viscous to transport the proppant articles 10 into the fracture 12 being created. The proppant particles 10 prevent the fracture 12 from closing when the pumping pressure is released. The proppant particles 10 are generally 20/40 to 12/18 mesh sand, bauxite, ceramic beads, etc. The proppant suspension and transport ability of the treatment base fluid traditionally depends on the type of viscosifying agent added.
Details about hydraulic fracturing can be found in the following references: Stimulation Engineering Handbook, John W. Ely, Pennwell Publishing Co., Tulsa, Okla. (1994); U.S. Pat. No. 5,551,516 to Normal et al.; “Oilfield Applications”, Encyclopedia of Polymer Science and Engineering, vol. 10, pp. 328-366 (John Wiley & Sons, Inc. New York, N.Y., 1987) and references cited therein, the contents of which are incorporated in their entirety.
When wells penetrating hydrocarbon-producing subterranean formations are produced, water often accompanies the oil and gas. The water, commonly referred to as “produced water”, can be the result of a water producing zone communicated with the oil and gas producing formation by fractures, high permeability streaks and the like. This may also be caused by a variety of other occurrences which are well known to those skilled in the art such as water coning, water cresting, bottom water, channeling at the well bore, etc.
It is known to use produced water as a fracturing fluid in the hydraulic fracturing process. In an offshore hydrocarbon recovery operation, injecting produced water into the injection wells is particularly desirable because dumping produced water into the sea may contaminate sea water given that the produced water contains hydrocarbon, emulsions, and solids contamination even after being treated. Using the produced water in hydraulic fracturing, however, may cause plugging of the injection wells due to the higher temperature of the produced water, the inclusion of emulsions and solid contamination. Despite the efforts to treat the produced water through surface treating facilities to remove the hydrocarbons and solid materials, there is still a small amount (<20 parts per million) of oil remaining in the produced water. With the high injection rates (e.g. 50,000 barrels per day) required in the offshore operation, these solids and hydrocarbon sludge can quickly accumulate on the pore throats of the formation taking the water.
When the pumps cannot deliver the required pressures to fracture the formations, resulting in the reduction of capacity to inject the produced water, a solution is to inject cold sea water, instead of produced water, into the injection well. Injecting the cold sea water, however, would change the rock properties and create small fractures called thermal fractures. These thermal fractures bypass the originally created fracture(s) and create a new injection path and are thus undesirable.
Therefore, it would be desirable to have methods which use produced water injection to enhance hydrocarbon recovery wherein the injection rates of produced water are improved while injectivity decline is minimized.